If by 3rd form you mean the past participle, then it is 'fallen'.
If you mean the second form, the Adult Spectrobe, get it to Lv.30 then make it eat an evolve mineral. TAHDA. If you mean the 3rd form, the evolved form, this is their last form and therefore cannot evolve further. ....(TAHDA.)
The 3rd form of "forward" is "forwarded."
"tiendra" is a form of the verb 'tenir', to hold, at the future tense, 3rd person singular.
Sceptile is Treekos 3rd Evolve form Steel-Cobra
comía is the 3rd person imperfect form of the verb comer (to eat). So, comía means: I used to eat.
It is a form (3rd per. sing.) of the verb revenir, which means to come back.
The third form of "flow" is "flowed."
Found
win
Sent
'Tarquin' is probably referring to a shortened form of the name 'Tarquinius', which was part of the name of the 3rd from last and last king of the Roman kingdom.